The present invention relates to an optical head for recording and reproducing information onto and from an information recording medium, and particularly to an optical head which is suitably used for optic integration.
Heretofore, there has been used, for example, an optical head as shown in FIG. 10. Light emitted from a laser diode 11 is turned into a parallel beam by a collimator lens 12. Then the emitted light beam is turned in its direction by a prism mirror lens 13, and is then focused onto an optical disc 15 by an objective lens 14. Light beam reflected from the surface of the optical disc is returned through the light path through which the emitted light beam is transmitted, and is further reflected by the combination of a quarter wavelength plate 16 and a polarizing beam splitter 17 to a focusing lens 18 for focusing the reflected light beam onto a photodiode 19, without being returned to the laser diode 11. Accordingly, information can be read from the disc.
However, the above-mentioned optical head in which lenses, mirrors and the like are three-dimensionally arranged, is not easily miniaturized or lightweight.
Accordingly, in order to make the optical head miniature or lightweight, an integrated optical head has been proposed as disclosed in Journal of the Institute of Electronics and Communication Engineers of Japan, Vol. J-86-C, 803, 1985, which is shown in FIG. 11. In this Figure, there are shown a semiconductor laser 21 as a light source, a light wave guide 22 for guiding light emitted from the semiconductor laser 21, a grating type focusing beam splitter 23 provided on the light wave guide 22, a focusing coupler 21 provided on the light wave guide 22, an optical disc 25, and a pair of light receiving elements 27 formed on an Si substrate 26. With the optical head as shown in FIG. 11, a light beam emitted from the semiconductor laser 21 transmits through the light wave guide 22 and is then incident upon the grating type focusing beam splitter 23. At this stage, zero-order light which is not diffracted is focused onto the optical disc 25 outside of the light wave guide 22 by means of the focusing coupler 24. Light reflected from the optical disc 25 is focused by the focusing coupler 24, and is transmitted through the light wave guide 22 in the direction reverse to the direction of the emitted light. Further, the direction of transmission of the reflected light is changed by the grating type focusing beam splitter 23, and is focused onto the two pairs of light receiving elements 27.
In the above-mentioned integrated optical head, a focusing and tracking drive mechanism which comprises a movable component composed of a drive coil and a permanent magnet, has to move the integrated optical head substrate in its entirety, and accordingly, it is difficult for the whole optical head including this drive mechanism to be miniaturized and lightweight and to be made to be cheap. Further, it is not suited to mass-production. That is, there has been a problem of insufficiently utilizing the advantages of the integrated optical head. Conventionally, there has been proposed an integrated optical head including a beam deflecting means which utilizes electro-optical effects or the like so as to integrate components corresponding to the above-mentioned drive components on a substrate. However, since this conventional integrated optical head uses a grating coupler as an objective lens, the diffraction of the focusing grating coupler varies with the deflection of the beam, and accordingly, focused beam aberrations occur.